Microsoft has released out-of-band security updates to address a remote code execution vulnerability — known as PrintNightmare (CVE-2021-34527) — in the Windows Print spooler service. The Computer Emergency Response Team Coordination Center (CERT/CC), part of the Software Engineering Institute at Carnegie Mellon University, last week reported a critical RCE vulnerability impacting the Windows Print Spooler service that allows a remote authenticated attacker to execute arbitrary code with system privileges on a vulnerable system.
The updates are cumulative and contain all previous fixes, as well as protections for CVE-2021-1675. The updates do not include Windows 10 version 1607, Windows Server 2012 or Windows Server 2016 — Microsoft states updates for these versions are forthcoming. According to CERT/CC, “the Microsoft update for CVE-2021-34527 only appears to address the Remote Code Execution (RCE via SMB and RPC) variants of the PrintNightmare, and not the Local Privilege Escalation (LPE) variant.” See CERT/CC Vulnerability Note VU #383432 for workarounds for the LPE variant.
The Cybersecurity & Infrastructure Security Agency encourages users and administrators to review the Microsoft security updates as well as CERT/CC Vulnerability Note VU #383432 and apply the necessary updates or workarounds. For additional background, see CISA’s initial communication.